High voltage bushings used within power transformers generally contain a quantity of dielectric oil for cooling and insulating the bushing electrodes. Over long periods of operation, the gas space above the surface of the oil dielectric can become contaminated by the gaseous byproducts of the decomposition of the insulation material used within the bushing. A sampling of the gaseous material in the space above the oil dielectric can therefore give an indication as to the condition of the oil dielectric and the paper dielectric materials within the bushing for incipient fault detection. Current means for sampling the gaseous materials existing above the oil dielectric generally involve surrounding the top portion of the bushing oil fill hole plug with an airtight enclosure and evacuating, then introducing the gaseous material to within the enclosure. There is often the question as to whether the atmosphere within the enclosure dilutes or otherwise affects the measured pressure and composition of the gaseous materials being tested.
The purpose of this invention is to describe methods and apparatus for rapidly and reliably obtaining samples of the gaseous materials existing above the oil dielectric in electrical bushings without the requirement for auxiliary housings or similar airtight enclosures.